Gripper chain conveyors are known in the paper handling industry. They provide reliable and deterministic paper handling by firmly clamping the material to be conveyed in a gripper attached to the chain, while the conveyor chain is in motion or is executing a motion profile. Some document inserter systems utilize a gripper chain that delivers envelopes from an envelope feeder/supply to an insertion station, and then onto a mailing output system for subsequent mail finishing. Motion of the gripper chain between the feeder, the insertion station and the output system is conducted in a stop/start incremental fashion.
A fundamental disadvantage to gripper chain conveyors is that, over time, the chain link pivots wear, resulting in chain stretch. As a chain stretches, there can be several undesirable effects for the apparatus described above. One example of an undesirable effect is that the at-rest insertion gripper position becomes unrepeatable with chain backlash. In another example, the slack side of the chain begins to oscillate aggressively resulting from the stop/start motion. The oscillation accelerates chain wear and possibly damages surrounding mechanisms.
Therefore, periodic chain tensioning is required to maintain reliable operation. For the apparatus described above, it is desirable to detect when there is sufficient chain stretch to warrant a re-tensioning operation to avoid these undesirable effects. Conventionally, re-tensioning and readjustment of the assembly is carried out once the insertion activity becomes unreliable or after the gripper chain causes damage to itself and/or surrounding mechanisms.